Petroleum well thermally activated safety relief device for differential pressure closing tubing safety valve



June 17, 1969 J. SLACK 3,450,202

PETROLEUM WELL THERMALLY ACTIVATED SAFETY RELIEF DEVICE FOR DIFFERENTIALPRESSURE CLOSING TUBING SAFETY VALVE Filed Jan. 25, 1968 Sheet .015 2Jryz 40 44 C) O V 40 40 40 INVENTOR k/O/M/ 54 9 c e ATTORNEY June v1969J. SLACK I 3,450,202

' PETROLEUM WELL THERMALLY ACTIVATED SAFETY RELIEF DEVICE FORDIFFERENTIAL PRESSURE CLOSING TUBING SAFETY VALVE Filed Jan. 25, 1968Sheet 5 of 2 INVENTOR c/o/wv 54 6 6K A ToRNaya Patented June 17, 1969US. Cl. 166-53 11 Claims ABSTRACT OF THE DISCLOSURE On a petroleum wellhaving a tubing safety valve in the tubing string, constructed to remainopen so long as the differential pressure across the valve does notexceed a predetermined amount and to close when the pressure dropexceeds said predetermined amount: a surface Well head element havingmeans defining at least one tortuous passageway therethrough, an innerend of the passageway being in communication vu'th the tubing stringbore and an outer end of the passageway being in communication with theatmosphere exteriorly of the well head; a plug of fusible material suchas lead is cast in situ in the tortuous passageway. The plug resistsextrusion from the passageway under high pressure and leakage of wellpressure around the plug; however, a fire in the vicinity of the surfacewell head element will melt the plug. opening its passageway. Thediameter of the passageway allows a sufficient flow rate to cause thepressure drop to exceed said predetermined amount, closing the valve andthus shutting in the well.

Background of the invention Tubing safety valves are commonly employedon petroleum wells and in many instances, especially on offshore wellsproduced from platforms, their use is required by law as a safetymeasure.

Several manufacturers currently market many variations of such tubingsafety valves. (E.g. note Composite Catalog of Oil Field Equipment &Services, 1966-67 edition, Gulf Publishing Company, Houston, variouspages, see index subheadings under Valves and various subheadings underChokes, especially ChokesStonm, and, for instance, pp. 3833-3844.) Somesuch safety valves are constructed to be mounted in the tubing stringeither as a segment of the string or as a pumped down, wire line loweredor sublowered element packed or latched in place in the tubing bore.Down hole tubing safety valves are usually mounted below the parafiinlevel so that periodic service or workover operations to remove paraffinfrom the tubing need not require removal of the tubing safety valves.The parafiin level differs from well to well and field to fielddepending on subterranean pressures and temperatures and on compositionof the base of the crude. As an example, it would not be unusual tomount a subsurface tubing safety valve about 2000 feet down in the well.

Other tubing safety valves are mounted at the surface, for instance onthe Christmas tree, and are sometimes referred to as automatic chokes.The device of the invention may also be used with them.

Tubing safety valves may be further categorized a cording to the mannerin which they are designed to be actuated. A first group, which may bereferred to as subsurface operated or differential pressure operated, isthe simplest, since ones in this group require no control linesextending to the surface. A typical valve of this type is normally open,and closes solely in response to attainment of a predetermined pressuredifierential across the valve either due to a pressure surge from belowthe valve or a failure of some well element above the valve, forinstance breakage of the Christmas tree due to wave action in a storm.

A second group of tubing safety valves may be referred to as beingsurface controlled. These, in addition to operating in response to asensation of attainment of a pressure drop of a predetermined magnitude,have control lines extending to a control point at the sunface w ere anoperator sensing danger, such as a fire or a violent storm, mayvoluntarily close the tubing safety Valve in order to forestall or limitthe consequences of a disaster.

The device of the invention may be used with both these types of tubingsafety valves.

With the advent of wells completed to produce from multiple zonesthrough the use of parallel tubing strings, it has become common toemploy a tubing safety valve for each tubing string.

Especially in instances where many wells are completed on a singleoffshore platform, the spectre of a disastrous fire has become a thingto be reckoned with. If the platform is tended, for instance bypersonnel drilling, completing or servicing other wells on the platform,a fire represents a risk to life, since sufficiently rapid evacuation byboat or helicopter may not be possible and swimming to safety may alsobe impossible. Even where a well platform is untended, a multiple wellfire could easily destroy millions of dollars worth of equipment and aloss of production of si'miar dollar magnitude. Such fires can resultfrom any of several sources, including lightning, equipment malfunctionand human error or negligence.

A problem which has become apparent, especially where well fires occurat wells having subsurface controlled tubing safety valves, is that evenafter a fire has gotten well under way, so that Christma tree packingmaterial has begun to burn and/or melt, allowing well fluids to escapeat the wellhead and feed the fire, often the pressure drop above thetubing safety valve caused by seal destruction is insufficient to allowthe tubing safety valve to close before additional wells catch fire.Thus the well continues to burn, endangering adjacent wells on thepatform and endangering personnel and the platform structure itself (seeComposite Catalog, op. cit., p. 3834, System 2, note 3).

To some extent, the problem just discussed may be overcome through useof tubing safety valves which may also be manually closed from thesurface; however, this is an imperfect solution since no one may bepresent near the manual control station at the time of the fire, thecontrol station may be unapproachable due to the fire, those present onthe platform who first see the fire may not know how to actuate thecontrol or may, through predominating fear for their own lives in arapidly worsening situation, decide to leave the platform as quickly aspossible before actuating the manual control.

Summary of the invention Because of the great pressures to which thefiow containing controlling members of a petroleum well tubing stringand Christmas tree are subject, for instance 10-20 thousand pounds persquare inch, the problem of providing a thermal activated system forclosing a petroleum well tubing safety valve is a more sophisticated onethan the routiner would be tempted to imagine.

The present invention provides, in a preferred emhodiment thereof, foruse in association with a petroleum well tubing string tubing safetyvalve constructed to remain open so long as the differential pressureacross the valve does not exceed a predetermined amount and to closewhen the pressure drop exceeds said predetermined amount: a surfacewellhead element having means defining at least one tortuous passagewaytherethrough, an inner end of the passageway being in communication withthe tubing string bore and an outer end of the passageway being incommunication with the atmosphere exteriorly of the well head; a plug offusible material such as lead is cast in situ in the tortuouspassageway. The plug resists extrusion from the passageway under highpressure, and leakage of well pressure around the plug; however, a firein the vincinity of the surface wellhead element will melt the plug,opening its passageway. The diameter of the passageway allows asufiicient flow rate to cause the pressure drop to exceed saidpredetermined amount, closing the valve and thus shutting in the well.

In the preferred embodiment, said wellhead element is an adapter bodyconnected to a lateral port of the Christmas tree. A specialplug-securing element is provided thereon to protect the device againstthe initial impact of exposure to the high pressure within the tubingstring.

The principles of the invention will be further hereinafter discussedwith reference to the drawing wherein a preferred embodiment is shown.The specifics illustrated in the drawing are intended to exemplify,rather than limit, aspects of the invention as defined in the claims.

In the drawing FIGURE 1 is an elevation view of part of a petroleumwell, illustrating apparatus elements according to the preferredembodiment of the invention;

FIGURE 2 is a longitudinal sectional view of the safety release deviceof FIGURE 1 taken substantially along the line 22 of FIGURE 3;

FIGURE 3 is an outer end view of the safety release device of FIGURES land 2; and

FIGURE 4 is a an inner end view of the safety release device of FIGURES1-3.

Description of the preferred embodiment The well shown in FIGURE 1 hasbeen typically provided with a surface casing 12 on which is mounted acasing head 14, for instance as shown on page 2067 of the CompositeCatalog. The casing head 14 receives and supports a hanger 16 in thebore thereof, for instance as depicted on page 2070 of the CompositeCatalog. A casing string 18 is connected near its upper end to thehanger '16 and supported thereby. A casing bonnet 20, for instance asshown on page 2073 of the Composite Catalog, surmounts the hanger 16 atthe upper end of the casing string 18. A tubing head 22, for instance asshown on page 7075 of the Composite Catalog, is mounted on the casinghead 14 via a contractileexpansible clamp 24, for instance, as depictedon page 2105 of the Composite Catalog.

A string of tubing 26 is hung in the well via a tubing hanger 28, forinstance as shown on page 2076 of the Composite Catalog. Lock screws 30received through lateral openings in the tubing head engage the upperend of the tubing hanger 28 and hold it down.

A tubing head bonnet 32 of the type shown on page 2083 of the CompositeCatalog is shown mounted on the top of the tubing head 22 via a clamp34, similar to the clamp 24. A tubular nipple 36 connects the throughbore of the tubing head bonnet 32 with the through bore of the tubinghanger 28.

A conventional master valve 38 is mounted on the tubing head bonnet 32via a clamp 40 similar to the clamps 24, -34. The conventional portionof the Christmas tree 42 is completed by a plurality of valves 44,gauges 46, plugs 48, clamps 40, Ts 50, a choke 52 and a Christmas treecap 54. The structure, use and reasons for the provision of suchelements will be understood by those skilled in the art from a review ofthe silhouettes shown in FIGURE 1.

The tubing string 26 in the well 10 is shown provided, below theparafiin level, with a pressure differential acti vated tubing safetyvalve 56 of conventional construction. The valve 56 is arranged toremain open so long as the pressure difference in the tubing stringabove and below the valve 56 does not exceed a predetermined pressure,for instance 300 p.s.i., and by way of example, may be as shown on page2836 of the Composite Catalog.

It should now be noticed that the tubing string bore is communicatedthrough the lateral outlet 58 of the T immediately above the mastervalve 38 to the upstream side of a thermal activated safety device 60(FIGURES 1-3) constructed in accordance with the present invention. Thedevice 60 is connected to the T 50 by a clamp 40. On its downstream sidea diverter pipe 62 is connected to the device 60 via a hub 64 on thepipe and a clamp 40 secured about the device 60 and hub 64. The diverterpipe functions to divert the flash of fire from the platform uponopening of the safety device 60; it extends pas-t the edge of theproduction platform, for instance to the flare line.

Before proceeding to discuss the device 60 in greater detail, it shouldbe noted that the ends of the parts secured by clamps 24, 34, 40 areprovided with frusto-conical sealing surfaces which receive and sealwith an oppositely tapered deflectable lip-sealing ring, for instance asshown in the commonly assigned earlier US. patents of Watts et al.,2,766,829; 2,766,998; 2,766,999; of Watts, 3,141,- 685; 3,216,746; ofLatham, 3,301,577; of Brown, 3,307,- 862; or of Latham et al.,3,325,176. A further example is provided on pages 2098-2099 of theComposite Catalog.

Now with more particular regard to FIGURES 2-4, the device 60 comprisesa generally cylindrical, spoolshaped body 66 of metal, for instance AISI1040 (90/60) steel. As an example of dimensions, the body 66 may beabout 5.25 inches long, have its central barrel 68 about 3.75 inches indiameter and wedging flanges 70 at its opposite ends about 4.75 inchesin diameter.

The wedging surfaces 72 on the flanges 70 are engaged by the clamps 40in securing the device 60 in position as shown in FIGURE 1.

Centrally of each axial end surface 74 of the body 66, a generallycylindrical recess 76, 78 is formed, having an axially outwardly flaringfrusto-conical sealing surface 80 closely adjacent the mouth thereof,for sealing with the exterior, frusto-conically tapered sealing surfaceof a sealing ring of the type aforementioned with reference to commonlyassigned earlier US. patents. These clamping and sealing connectormeans, although preferred for use in the present instance because oftheir accepted trustworthiness under operating conditions at highpressures, are exemplary.

Centrally of the floor 82 upstream recess 76, a socket 84 is formed inthe body coaxially therewith and opening outwardly of the floor 82. Forthe major portion of its length, the socket 84 is internally threaded at86; axially inwardly of the threaded portion, the socket 84 has a shortcylindrical region 88, merging with a tapering frustoconical region 90,which in turn terminates in a circular, disk-shaped floor 92 coaxialwith the body 66.

Three equiangularly spaced, axially directed passageways 94, 96, 98 areshown formed in the body 66 through the floor 92; these extend part waytoward the downstream recess 78 floor 100. In the example, the passageways 94, 96, 98 are centered on a circle of A inch radius. Threeequiangularly spaced, axially directed passageways 102, 104, 106 areshown formed in the body 66 through the downstream recess 78 floor 100;these extend part way toward the upstream recess 76. The passageways 94,96, 98 are angularly offset from respective of the passageways 102, 104,106 by about 60 degrees. In other words, the passageway 96 lies abouthalfway angularly between the passageways 104 and 106. The passageways94, 96, 98 extend axially to lateral adjacency with and somewhat axiallybeyond the inner ends of the passageways 102, 104, 106 as shows best inF[GURE 2. The passageways 102, 104, 106 are centered on a circle of /sinch radius.

A lateral passageway 108 formed in the body 66 intermediate the endsthereof intersects the passageways 94 and 102 near their inner ends. Theouter end of the passageway 108 is threaded at 110 and provided with anexteriorly threaded plug 112 to close off the outer end. Thus a tortuousor labyrinthine passageway 94, 102, 108 is provided which communicatesbetween the upstream and downstream axial ends of the body 66. Thetortuousness of the passageway 94, 102, 108 is contnibuted to by theshort axial extensions of the passageways 94 and 102 past the connectingpassageway 108 and the short portion of the passageway 108 which extendsbetween the passageway 102 and the inner end of the plug 112.

A second lateral passageway 114 formed in the body 66 intermediate theends thereof intersects the passageways 96 and 104 near their innerends. The outer end of the passageway 114 is threaded at 116 andprovided with an exteriorly threaded plug 118 to close off the outerend. Thus a second tortuous or labyrinthine passageway 96, 104, 114 isprovided which communicates between the upstream and downstream axialends of the body 66. The tortuousness of the passageway 96, 104, 114 iscontributed to by the short axial extensions of the passageways 96 and104 past the connecting passageway 114 and the short portion of thepassageway 114 which extends between the passageway 104 and the innerend of the plug 118.

A third lateral passageway 120 formed in the body intermediate the endsthereof intersects the passageways 98 and 106 near their inner ends. Theouter end of the passageway 120 is threaded at 122 and provided with anexteriorly threaded plug 124 to close off the outer end. Thus a thirdtortuous or labyrinthine passageway 98, 106, 120 is provided whichcommunicates between the upstream and downstream axial ends of the body66. The tortuousness of the passageway 98, 106, 120 is contributed to bythe short axial extensions of the passageways 98 and 106 past theconnecting passageway 120 and the short portion of the passageway 120which extends between the passageway 106 and the inner end of the plug124.

The passageways 94, 102, 108; 96, 104, 114 and 98, 106, 120 are eachabout A-inch in diameter; thus these passageways have a collective,total transverse cross-sectional area of about .147 inch and a volume ofabout .598 cubic inch.

Prior to installation in the Christmas tree as shown in FIGURE 1, a lowtemperature melting, soft metal composition 126 is poured in a liquidcondition into the passageways 94, 102, 108; 96, 104, 114 and 96, 106,120, filling the same and is allowed to cool, congeal and solidifytherein. Surplusage of the composition 126 is machined away from theregion 88, 90, 92, and in fact, these surfaces may be finish machined onthe body after the composition 126 is in place. A disk or annulus of lowtemperature melting, soft metal composition 128 correspondinglyconfigured to the surfaces 90, 92 is inserted in the dish so defined.The element 128 in the example is about /8 inch thick, 1 inches indiameter at its larger diameter end and 1 inches in diameter at itssmaller diameter end.

A steel washer 130 having an OD. approximating the larger diameter ofthe element 128 is placed against the larger diameter end of the element128. The steel washer 130 has an I.D. large enough to encompass thethree passageways 92, 94, 96. The element 128 is forced tightly againstthe surfaces 90, 92 by an elongated tubular nut 132, exteriorly threadedat 134 so as to be threadable into the socket 84 at 86 and tightenableby application of a wrench to the external wrenching region 136 of theelongated nut. The ID. of the nut is also large enough to encompass thethree passageways 94, 96, 98.

In the example, the metal poured into the passageways of the device 60consists of lead. The cover wafer 128 is made of the same material. Themelting point of lead is 621 F. It has been found that when the pressuredifferential upstream and downstream of the device 60 is 10,000l5,000p.s.i. the lead of the wafer 128 and in the passageways will extrude outof the passageways, opening them when the temperature of the device 60has reached 325 degrees Fahrenheit. Should thermal activation at higheror lower temperatures be desired the lead of the example may be partlyor wholly replaced or supplemented with other materials such as bismuth,antimony, tin, and the like, as alloys or as mixtures.

With some compositions, it may be possible to pour the passagewayfilling and wafer 128 as an integral ainit. However, it has been foundthat where the composition shrinks somewhat upon cooling, the initialimpact of high pressure upon the wafer, after the device has beeninstalled as in FIGURE 1, may cause highly undesirable fluid pressureleaks between the wafer/passage filling integral unit and the socket andpassageways. The separate wafer 128 inserted after machining of thedevice 60 as described above, tightened into place with the elongatednut 132 (with the steel washer 132 interposed therebetween to preventgouging of the wafer by the nut) forms a positive seal which will notleak when high pressure is applied thereto.

It should now be apparent that when the device 60 of FIGURES 2-4 isinstalled in a Christmas tree as exemplified by the tree of FIGURE 1,and its upstream side communicated to the tubing string pressure, a fireat the wellthead will cause the fusible or flowable material in the body66 socket and passageways to extrude, flow or melt out being then pusheddownstream by the well pressure, opening the passageways through thedevice 60. The combined cross sectional area of the passageways, whenopened, is more than enough to cause the predetermined pressure dropwhich will close the tubing safety valve, shutting in the well. Anyblast or pressure surge which might momentarily occur as the passagewaysopen, just before the tubing safety valve closes, is carried safely fromthe well platform by the diverter pipe 62.

The tortousness of the device 60 passageways is needed to ensure thatpremature extrusion of the filling material will not occur due to thehigh pressure to which the upstream side of the device is subject duringuse and in view of the relatively plastic nature of the fillingmaterial.

Of course there is nothing mystic about the provision of threepassageways 94, 102, 108; 96, 104, 114 and 98, 106, any number from oneto several of such passages may be provided, so long as they aresufficiently tortuous that the filling material will not extrude fromthem prematurely, i.e. before a fire, and so long as their effectivetransverse cross-sectional area, when opened, is sufficient to allow thepressure drop needed to close the tubing safety valve to occur.

It should be noted that the device of the invention does not inhibit orinterfere with the operation of the tubing safety valve as a means forautomatically or manually limiting the flow rate of fluid being producedfrom the well.

The particular location of the device 60 on the Christmas tree of FIGURE1 was chosen so that it does not interfere with the normal operation,servicing and repair of other elements on the Christmas tree, and sothat it may be checked and replaced itself without need for disturbingproduction or requiring a major dismantling effort. However, theparticular relative location is exemplary and other relative locationswill occur to those skilled in the art.

It should now be apparent that the petroleum well thermal activatedsafety relief device for differential pressure closing tubing safetyvalve as described hereinabove possesses each of the attributes setforth in the specification under the heading Summary of the Inventionhereinbefore. Because the petroleum well thermal activated safety reliefdevice for differential pressure closing tubing safety valve of theinvention can be modified to some extent without departing from theprinciples of the invention as they have been outlined and explained inthis specification, the present invention should be understood asencompassing all such modifications as are within the spirit and scopeof the following claims.

What is claimed is:

1. For employment on a petroleum well having a tubing safety valve in atubing string thereof, which tubing safety valve is constructed toremain open so long as the differential pressure across the valve doesnot exceed a predetermined amount and to close when the pressure dropexceeds said predetermined amount: a surface well head element havingmeans defining at least one tortuous passageway therethrough, an innerend of the passageway being in communication with the tubing string boreand an outer end of the passageway being in communication with theatmosphere exteriorly of the well head; a body of hardened, heatsoftena'ble material filling said passageway and being susceptible tosoftening and flowing out of said passageway upon the occurrence of afire in the vicinity of said well head element; the effectivecross-sectional area of said passageway, when so opened, beingsufficient to cause said predetermined pressure drop, thereby closingthe valve and shutting in the petroleum well.

2. The apparatus of claim 1 wherein the hardened, heat softenablematerial is lead.

3. The apparatus of claim '1, wherein said at least one passagewaycomprises a first axially extending segment beginning at the inner endof said passageway and terminating intermediate the extent of saidpassageway through said well head element; a second axially extendingsegment beginning at the outer end of said passageway and terminatingintermediate the extent of said passageway through said well headelement; said first and second segments being out of axial registry andextending to lateral adjacency with one another; and a lateralpassageway segment connecting said first and second axially extendingsegments intermediate the extent of said passageway through said wellhead element.

4. The apparatus of claim 3 wherein said at least one passageway furthercomprises at least one further passageway geometrically substantiallylike the first described passageway and being laterally displaced fromthe first described passageway within said well head element.

5. The apparatus of claim 4 wherein said well head element is generallycylindrical; means defining a recess in at least the upstream axial endof said well head element; means defining a socket in said recess,opening toward said upstream axial end and having means defining afloor; the inner ends of said passageways opening through said floor; aclosely fitting wafer of hardened, heat softenable material received insaid socket against said floor covering the inner ends of saidpassageways.

6. The apparatus of claim 5 wherein said passage filling, hardened, heatsoftenable material is hardened in sim in said passageway; said waferbeing separate from said passage filling, hardened, heat softenablematerial; said socket, axially beyond said wafer being providedinternally with axially proceeding, incrementally usable cooperativesecurement means; and a tubular fastening element having external,axially proceeding, incrementally usable cooperative securement meansthereon coopera-ble with the first-mentioned said cooperative securementmeans to force said wafer into sealing engagement with said socketfloor.

7. The apparatus of claim 6 wherein said wafer is peripherallytrust-conical exteriorly and wherein said socket, adjacent said socketfloor is interiorly peripherally frustoconical in conformance with saidwafer and wherein said tubular fastening element bears against thelarger diameter 'face of said Wafer near the periphery thereof, forcingsaid frusto-conica1 peripheries into sealing engagement.

8. The apparatus of claim 6 wherein the cooperative securement meanscomprise helical threading and the tubular fastening element compriseson elongated tubular nut heaving said helical threading thereon near oneend thereof and having a wrenching region thereon near the opposite endthereof; the bore of said elongated tubular nut encompassing the innerends of said passageways, and said elongated tubular nut bearing againstsaid wafer.

9. The apparatus of claim 8 further comprising a steel washer interposedbetween the elongated tubular nut one end and said wafer; said elongatedtubular nut one end engaging said steel washer and said steel washerengaging said wafer.

10. A petroleum well including at least one string of production tubing;a tubing safety valve in communication with the bore of said string ofproduction tubing, said tubing safety valve being constructed to remainopen so long as the differential pressure across the valve does notexceed a predetermined amount and to close when the pressure dropexceeds said predetermined amount; a surface well head element havingmeans defining at least one tortuous passageway therethrough, an innerend of the passageway being in communication with the tubing string boreand an outer end of the passageway being in communication with theatmosphere exteriorly of the well head; a body of hardened, heatsoftenable material filling said passageway and 'being susceptible tosoftening and flowing out of said passageway upon the occurrence of afire in the vicinity of said well head element; the effectivecrossse'otional area of said passageway, when so opened, beingsufficient to cause said predetermined pressure drop, thereby closingthe valve and shutting in the petroleum well.

11. The petroleum well of claim 10 further comprising a diverter pipesecured to said well head element in communication with the outer end ofsaid at least one passageway, said diverter pipe extending a substantialdistance away from said well to divert flame and combustibles therefromupon opening of said at least one passageway.

References Cited UNITED STATES PATENTS 1,880,778 10/1932 Byers 166532,104,660 1/1938 Long, et al 166-53 X 3,377,957 4/1968 Bil-ton 137-74 XFOREIGN PATENTS 93,165 10/ 1938 Sweden.

DAVID H. BROWN, Primary Examiner.

US. Cl. X.R. 137-74; 166-67

